It is proposed to study the participation of upper airway (UAW) muscles during sleep-apnea in immature & adult potoroos, an Australian marsupial. Such an investigation permits an identification of respiratory arrest due to 1) functional obstruction in the UAW, e.g. glottic closure or tongue relapse during inspiratory effort (diaphragmatic contractions) or 2) cessation of respiratory effort diaphragm, intercostals & abdominal) with or without activation of UAW muscles. During anesthesia animals of different (pouch) ages are implanted with suitable recording electrodes to monitor electrophysiologically states of vigilance. Adult potoroos. The EMG of the following muscles are recorded: diaphragm, intercostal, supra- & infrahyoid; EMG of laryngeal muscles: posterior cricoarytenoid, thyroarytenoid & lateral cricoarytenoid. The above are recorded on a Grass Model 7 Polygraph. The effects of breathing high concentrations of CO2 and low O2 concentrations in different states of vigilance. Pouch young. Using electrophysiological techniques to detect sleep-waking states, the EMG of diaphragm, intercostals, abdominal & suprahyoid muscles is recorded from the immature within the mother's pouch (pre-weaning period). The effects of changing respiratory gas composition on the young in marsupium is also studied. The etiology of sudden infant death is presumed to be due to malfunctions of neural controls of respiration. The proposed study holds promise for elucidating the normal mechanisms governing the interrelations of sleep and respiration. The experimental animal to be used has the advantage of pursuing studies on a mammal in a very immature state yet having the ability to maintain its own respiration. The developing young are readily accessible at the pouch of a docile female maintaining the young's body temperature, water and nutritional requirements and in which the sleep-awake rhythm of the young is unaffected by that of the mother. Our past experience with this biological model and work on small mammals (rat) places us in a unique position to provide findings of considerable physiological and clinical significance.